Molecules of life

Carbohydrates, proteins, lipids (or fats) are major nutrients that we need in large quantities.

We get these by eating them. They are broken down first and then reassembled into our own carbohydrates, proteins and lipids. This is because:

  • most of the molecules in food are too large to pass through the absorbing surface of the gut wall
  • the carbohydrates, proteins and lipids are reassembled in the form required, rather than other animal or plant versions
NutrientMajor functionMajor sources
CarbohydratesSource of energy, glucose is the main respiratory substrateStarch: potatoes, rice and wheat products, bread, cereals and pasta. Sugars: fruit, smoothies, fizzy drinks, chocolate and sweets
ProteinsGrowth and repairMeat, eggs, cheese, beans, nuts and seeds
LipidsEnergy, make up part of cell membranes so essential for normal growthButter and margarine, meat and processed meat, plant oils, oily fish, nuts and seeds